Method of operating oil-cracking retorts



June 12, 1945. R. MycHATTERTN ET Al.

METHOD 0F OPERATING GIL-CRAGKING REToRTs Filed July 27, 1942 :mean-z.

Patented June 12, 1945 METHOD or' OPERATING ola-cancinuc aa'roars RollinM. Chatterton, Malden, Mass., and Walter V C. Slade, Providence, B. I.,`asslxnors to Fuel Research Development Corporation, Boston, Mass., acorporation of Massachusetts Application July zr, 1942, semi Ne. 452,4544 Claims. (Cl. llil-2025) Y This invention relates te externally heatedretorts used in the continuous manufacture of cary bureted water gas.lOur present invention relates more specifically to the provision of animproved method of operation for such retorts, by which method the lossof time previously required for the removal of carbon deposited on theretort walls may be eliminated.

Our invention further relates to certain ordered procedure which will behereinafter described and more particularly pointed out in the appendedclaims.

A retort adapted for the carrying out of our improved method ofoperation is shown in the drawing, which is a sectional front elevationof an externally heated retort. The retort comprises an inner casing Iwhich is preferably enlarged downwardly and which is supplied withfragmentary refractory material C from a hopper I2 through a feed pipeI4 by a charging device I5. The refractory material C travels slowlydownward through the retort during the operation thereof and iscontinuously removed from the lower end of the retort by a dischargingdevice I6.

The retort I0 is enclosed within an outer casing 20, and the spacebetween the retort I0 and the i casing is divided by baffles orpartitions 2| into a. series of heating ilues 22, adapted to'receive hotcombustion gases or other heating media from a suitable source ofsupply.

An oil feed pipe is inserted in the upper end ef the retort I0 andextends downward into the upper portion of the refractory material, asclearly shown in the drawing. The rate of oil feed may be controlled bya suitable valve 2B. A gas delivery pipe 28 is provided at thev upperend of the retort I0 for removal of the carbureted water gas and othergaseous products of the retort. A steam pipe 30, controlled by a valve 3I, provides for admission of steam at the lower end of the retort, for apurpose to be described.

When the retort is in operation', the refractory material C is highlyheated by `the external vapplication of heat in the flues 22, and oiladmitted through the pipe 25 is cracked in the presence of the heatedrefractory, Awith production of oil gases and vapors and with deposit ofoil carbon on the refractory.

As the refractory material with the deposited carbon travels downward inthe retort, steam is admitted through the pipe I0 and reacts with thecarbon in the lower portion of the retort to produce water gas, whichthen passes up through the retort and refractory and is enriched andcarbureted by mixture with the oil gases and vapors produced by thecracking of oil in the upper part of the retort. The unconsumed carbondeposited on the' refractory material continues to move downward and iseventually removed from the retort by the discharging device I6.

A retort having the general construction and operation above set forthis disclosed in the prior` application of Chatterton and Paffen, SerialNo. 332,154, filed April 20, 1940, and to which reference is made formore detailed disclosure.

In normal operation, the temperature in the oilcracking zone issubstantially below the temperature in the water-gas-making zone.operating temperatures may be around 1100" F. in the oil-cracking zoneand around 1600" F. in the water-gas-making zone, with maximumtemperatures in similar relation.

1n the operation of a retort as above described, it is found that thegreater part of the oil carbon from the cracking operation is depositedon the downwardly moving refractory. A small part of the carbon iscarried upward with the water gas and oil vapors and passes out of theretort through the gas delivery pipe '28. There is a marked tendencyalso for the oil gases and vapors to move upward around the periphery ofthe retort and adjacent the inner surface of the retort wall, as passagefor the gases is commonly more free and open adjacent the retort wallthan in the body of the refractory material, The oil vapors coming incontact with the hot retort wall are cracked with the deposit of somecarbon thereon.

Consequently, while the bulk of the oil carbon is deposited on therefractory material and some of it passes off with the gases, aconsiderable amount is deposited on the inner surface of the retort, asindicated at D in the drawing, and this vlatter deposit gradually buildsup and increases in thicknesses until it interferes with the freedownward travel of the refractory. Furthermore, the carbon` thusdeposited is a poor conductor of heat and reduces the transfer of heatto the cracking zone of the retort, with corresponding reduction in theoil-cracking capacity of the retort.

It has been found in' actual practice that the carbon will accumulate onthe retort wall in a matter of ten days to two weeks to such an extentas to require complete shutting down of the retort for cleaning. Theusual method of removing deposited .carbon from a retort wall is thesoc'alled scurflng. operation that is in common use in coal gas plants.It consists in emptying the retort as; completely as possible, and thenpassing air up through the retort to burn the deposited carbon from thewall. In an oil-crackins Minimum retort, this scuriing operationrequires two or more days at intervals of ten days to two weeks. andduring this time the retort is completely out of production. Burning thedeposited carbon with air also subjects the retort walls to excessivetemperature changes and endangers the retort structure.

In our improved method of operating an oilcrackingretort, we avoid thisshutting down of the retort, with attendant loss `oi' time, byproceeding in the following manner:

After the retort has been in operation in the usual way in thecontinuous manufacture of carbureted water gas for a relatively shortperiod, such as three or four days, we change the method of operation byclosing the valve 28 and shutting oil the oil supply to the retort, andusually vby increasing the supply of steam through the pipe 30. Thedownward feed of the refractory material is also preferably stopped orat least substantially reduced.

As the oil normally acts as a cooling medium in the upper part of theretort. the retort wall and the carbon deposited thereon become morehighly heated after the oil is shut on' and the upper part of the retortattains water-gas-makingtemperatures. At the same time, the steam risingthrough the retort becomes superheaed. This superheated steam thendirectly attacks the deposited oil carbon, consuming the carbonandforming water gas therefrom, which gas passes out through the usual gasdelivery pipe 28.

By continuous operation in this manner for a relatively short period,such as twenty-four hours, the oil carbon on the retort wall will besubstantially consumed and the retort will then be in satisfactorycondition for further manufacture of carbureted water gas. Oil is thenagain admitted through the pipe 25, the amount of steam admitted throughthe pipe 30 is somewhat reduced, and the manufacture of carbureted watergas is resumed for a further considerable period.

In this manner, carbureted water gas will be continuously produced in anexternally heated retort during the major tion, and uncarbureted waterduced while the oil carbon on being consumed and removed. y

In actual commercial operation, the retorts are commonly provided inbenches of perhaps eight retorts, and our improved method may beconveniently carried out by operating successive pairs of retorts fortwenty-four hour periods each in the manufacture of uncarbureted watergas and removal of deposited oil carbon from the retort wall, while theremaining six retorts are producing carbureted water gas. The volume ofgas produced in a retort by each of the two methods of operation isusually substantially the same.

The heating value of the carbureted water gas as generally made in theoil-cracking retorts is considerably higher than the usual commercialstandard for manufactured gas. By operating a part of the retorts in abench to make uncarbureted water gas and mixing this with the carburetedWater gas from the remaining retorts, the resulting mixed gas from allof the retorts in a bench may be made to equal any of the usualstandards for the heating value of manufactured gas. During the firstpart of the cleaning period, the water gas continues to be enriched to aconsiderable extent by the vaporization and cracking of the oil alreadydeposited in the refractory material and oil carbon at the time ofclosing the valve 2l in the oil feed pipe.

gas will be prothe retort wall is part of the time of opera- Byoperating in this manner, a bench of retorts may be operated-for anindefinite period to produce a mixture of uncarbureted water gas andcarbureted water gas, which mixture has characteristics suitable forcommercial service.

As an alternative method of operation, enough excess external heat maybe supplied to the upper part of the retort to raise the temperature ofthe deposited carbon to that required for making water gas withoutshutting olf the oil feed. By passing more steam up through the retortthan will react with the carbon deposited on the refractory material aportion of the excess stream will react with the highly heateddepositedcarbon to form water gas, thus removing the deposited carbon from theretort wall.

Having thus described our invention and the advantages thereof, we donot wish to be limited to the details herein disclosed, otherwise thanas set forth in the claims, but what we claim is:

1. The method of operating an externallyheated upright oil-crackingretort which comprises moving a mass of fragmentary refractory materialcontinuously downward through said retort, feeding oil into the upperpart ci said refractory mass,-externally heating the retort and therebyheating said refractory to crack said oil, with deposit of oil carbon onsaid refractory and on the inner surface of the retort wall, admittingsteam in the lowerpart of said retort to react with the oil carbondeposited on the refractory and to form water gas therefrom, carburetingand enriching said water gas by mixing said water gas with the oil gasesand vapors produced by cracking the oil, increasing the external heat toraise the temperature of the retort wall and of the carbon depositedthereon to water-gas-making temperature when said deposit has attained asubstantial thickness, and providing an increased flow of steamsufficient to effectively coact with the carbon deposited both on theretort wall and on the refractory, whereby said oil carbon on saidretort wall becomes more highly heated and reacts with that part of saidsteam which is in excess of that which will react with the carbondeposited on the refractory to produce water gas, and said oil carbonbeing thereby removed from said retort wall with the production ofadditional water gas.

2. The method of operating an externallyheated upright oil-crackingretort which comprises moving a mass of fragmentary refractory materialcontinuously downward through said retort, feeding oil into the upperpart of said refractory mass, externally heating the retort and therebyheating said refractory to crack said oil, with deposit of oil carbon onsaid refractory and on the inner surface of the retort wall, admittingsteam in the lower part of said retort to react with the oil carbondeposited on the refractory and to form water gas therefrom, carburetingand enriching said water gas by mixing said water gas with the oil gasesand vapors produced by cracking the oil, increasing the external heat toraise the temperature of the retort wall and of the carbon depositedthereon to water-gasmaking temperature when said deposit has attained asubstantial thickness, reducing the rate of downward travel of therefractory material, and providing an increased ilow of steam sufilcientto effectively react with the carbon deposited both on the retort walland on the refractory, whereby said oil carbon on said retort wallbecomes more highly, heated and reacts .with that part of said steamwhich is in excess of that which will react with the carbon deposited onthe refractory to produce water gas, and said oil carbon being therebyremoved from said retort Wall with the production of additional Watergas.

3. The method of operating an externallyheated upright oil-crackingretort which comprises feeding a mass of fragmentary refractory materialthereto and moving said material continuously downward through saidretort, feeding oil into the upper part of said refractory mass,externally heating the retort and thereby heating said refractory tocrack said oil, with deposit of oil carbon on said refractory and on theinner surface of the retort, simultaneously admitting steam in the lowerpart of said retort to react with the oil carbon deposited on therefractory and to form Water gas therefrom, carbureting and enrichingsaid water gas by mixing said'water gas with the oil gases and vaporsproduced by cracking the oil, shutting off the oil supply when thedeposit of oil carbon o n the retort wall has attained a substantialthickness but maintaining an adequate steam supply, and continuing theexternal heating, whereby said oil carbon on said retort wall becomesmore highly heated and reacts with said steam supply to produce Watergas, said oil carbon being thereby consumedv and removed and said retortwall being effectively cleaned.

4. The method of operating an externally-v heated retort as set forth inclaim 3, in which the continuous downward feed of the refractorymaterial is interrupted during the removal of the oil carbon depositedon the retort wall.

ROLLIN M. CHA'ITERTON. WALTER C. SLADE.

